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  Electro-optic display and manufacturing method thereofUSPTO Application #: 20060289866Title: Electro-optic display and manufacturing method thereof Abstract: A pixel electrode is disposed to cover the inner surfaces of a pixel-drain contact hole passing through a third insulating film and a second insulating film to reach a drain electrode. At the bottom of the pixel-drain contact hole, the pixel electrode is electrically connected with the drain electrode through a contact conductor film. The pixel-drain contact hole is formed of a connection of a contact hole passing through the second insulating film and a contact hole passing through the third insulating film. The dimensions of the opening end of the contact hole are larger than its dimensions at the bottom, and thus the inner surfaces of the contact hole are smoothly sloped and shaped like a crater in cross section. (end of abstract) Agent: C. Irvin Mcclelland Oblon, Spivak, Mcclelland, Maier & Neustadt, P.C. - Alexandria, VA, US Inventor: Toshio Araki USPTO Applicaton #: 20060289866 - Class: 257059000 (USPTO) Related Patent Categories: Active Solid-state Devices (e.g., Transistors, Solid-state Diodes), Non-single Crystal, Or Recrystallized, Semiconductor Material Forms Part Of Active Junction (including Field-induced Active Junction), Amorphous Semiconductor Material, Field Effect Device In Amorphous Semiconductor Material, In Array Having Structure For Use As Imager Or Display, Or With Transparent Electrode The Patent Description & Claims data below is from USPTO Patent Application 20060289866. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to electro-optic displays and manufacturing methods thereof, and particularly to an active-matrix electro-optic display having thin film transistors (TFTs) as switching elements, and to a manufacturing method thereof. [0003] 2. Description of the Background Art [0004] As electro-optic displays using liquid crystal or organic-electroluminescence (EL) as electro-optic elements, active-matrix TFT-array substrates (active-matrix substrates) are widely used in which an array of switching elements, such as thin film transistors, is formed on the substrate and an independent video signal is applied to each display pixel. [0005] In such an electro-optic display, it is important to make the display area of each pixel as large as possible, or to use a substrate with a high aperture ratio, in order to obtain bright and high display quality. [0006] Japanese Patent Application Laid-Open No. 10-170951 (see FIGS. 1 and 2, hereinafter referred to as Patent Document 1) discloses a common structure of such an active-matrix substrate with a high aperture ratio. [0007] In the active-matrix substrate disclosed in the Patent Document 1, gate signal lines, gate insulating film, semiconductor film, and source and drain electrodes electrically connected to the semiconductor film are sequentially formed to fabricate TFTs on a transparent insulative substrate, e.g., glass. Then, the entire substrate including the TFTs is covered with an inorganic insulating film and further with an organic interlayer insulating film, which is followed by planarization. This structure allows the pattern of pixel electrodes to be overlapped with signal lines. This enhances the aperture ratio of the liquid crystal display and makes it possible to shield electric fields caused by signal lines. [0008] In the active-matrix substrate disclosed in the Patent Document 1, a contact hole for electrically connecting the pixel electrode and the drain electrode of the TFT located under the pixel electrode is formed by etching the inorganic insulating film using the organic interlayer insulating film as a mask. [0009] In this case, the edges of the inorganic insulating film that define the bottom of the contact hole are located in a position further inside in the plane direction than the edges of the organic interlayer insulating film existing thereon, and then the organic interlayer insulating film may project like eaves beyond the inorganic insulating film. [0010] This phenomenon occurs because the inorganic insulating film is somewhat over-etched so that the drain electrode is exposed in the bottom of the contact hole. Then, the pixel electrode cannot cover the eave-like portions at the bottom of the contact hole, which results in disconnection. [0011] Also, in a liquid crystal display, electrically connecting an upper electrode and a lower electrode through a contact hole passing through an interlayer insulating film may encounter another problem as described in Japanese Patent Application Laid-Open No. 2004-233683 (see FIG. 12(b): hereinafter referred to as Patent Document 2). [0012] That is, according to the Patent Document 2, when the pixel electrode is made of transparent material such as ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide), the pixel electrode is prone to crack and disconnect on the organic interlayer insulating film at the peripheral edges of the contact hole. [0013] In order to solve this problem, Patent Document 2 discloses a partially two-layered structure in which first and second pixel electrodes are stacked in the contact hole and its vicinity. [0014] The inventors of the present invention examined the above-described problems of conventional liquid crystal displays and found that the formation of cracks on the organic interlayer insulating film at the peripheral edges of the contact hole can be avoided by smoothly tapering the peripheral edges of the contact hole or by forming at least the first pixel electrode not with oxide such as ITO and IZO but with ductile metal, for example. [0015] Even when the first pixel electrode is made of a film of opaque metal, no problem arises with light transmission in the pixel area when the second pixel electrode is made of transparent material, because the first pixel electrode is disposed only in the contact hole and its vicinity. [0016] However, it has been found that, when the first pixel electrode as the lower layer of the partially two-layered pixel electrode is made of a metal film, the edges of the metal film are likely to be reversely tapered in cross section, and then the overlying second pixel electrode may be disconnected in the reversely tapered portion. [0017] The metal film is reversely tapered in cross section because the metal film is etched by etching liquid penetrating the interface between the metal film and the underlying organic interlayer insulating film. SUMMARY OF THE INVENTION [0018] An object of the present invention is to provide an electro-optic display and its manufacturing method which prevent point defects caused by disconnection between overlying pixel electrodes and underlying TFT drain electrodes. [0019] According to the present invention, an electro-optic display includes an active-matrix substrate having an insulative substrate and a plurality of display pixels arranged in a matrix on the insulative substrate and each having a pixel electrode electrically connected with a thin film transistor, wherein, in each of the display pixels, the active-matrix substrate further includes: an inorganic insulating film that entirely covers an upper surface of the insulative substrate including a drain electrode of the thin film transistor; an organic resin insulating film that entirely covers an upper surface of the inorganic insulating film; a pixel-drain contact hole that passes through the inorganic insulating film and the organic resin insulating film to reach the drain electrode; and a contact conductor film that is provided at the bottom of the pixel-drain contact hole and is in contact with the drain electrode, and the pixel electrode is disposed to cover an upper surface of the organic resin insulating film and also to cover an inner wall of the pixel-drain contact hole and the contact conductor film. [0020] According to the electro-optic display, the contact conductor film is in contact with the drain electrode at the bottom of the pixel-drain contact hole, and the pixel electrode covers the organic resin insulating film and also covers the inner walls of the pixel-drain contact hole and the contact conductor film. Accordingly, when the contact conductor film is made of a thin film of metal having higher ductility than transparent conductive film material such as ITO, for example, it is possible to prevent the contact conductor film from cracking so as to prevent point defects caused by disconnection between the pixel electrode and the underlying TFT drain electrode. Also, electrically connecting the pixel electrode and the drain electrode through the contact conductor film reduces the resistance of connection and provides an electro-optic display of high display quality. Furthermore, the contact conductor film is made of material capable of making electric contact with the drain electrode and the pixel electrode, which offers a wider choice of the material of the drain electrode. [0021] The present invention also provides a method of manufacturing an electro-optic display including an active-matrix substrate having an insulative substrate and a plurality of display pixels arranged in a matrix on the insulative substrate and each having a pixel electrode electrically connected with a thin film transistor, and the manufacturing method includes the following steps (a) to (g). The step (a) is to form an inorganic insulating film entirely covering the upper surface of the insulative substrate including a drain electrode of the thin film transistor. The step (b) is to form an organic resin insulating film entirely covering the upper surface of the inorganic insulating film. The step (c) is, in a portion of the organic resin insulating film that is located above the drain electrode, to form a first opening passing through the organic resin insulating film to reach the inorganic insulating film, and a second opening sized larger than the first opening and located concentrically with the first opening, the second opening not passing completely through the organic resin insulating film, so that part of the organic resin insulating film remains under the bottom of the second opening. The step (d) is to etch the inorganic insulating film using the first opening as a mask to form a first contact hole passing through the inorganic insulating film. The step (e) is to perform an ashing process using oxygen to thin the entirety of the organic resin insulating film and to form a second contact hole passing through the organic resin insulating film by processing the second opening so that its inner walls smoothly slope to be shaped like a crater in cross section with its opening size increasing from the bottom toward the opening end, thereby forming a pixel-drain contact hole including the first and second contact holes communicative connected to each other. The step (f) is to form a contact conductor film filling the first contact hole at the bottom of the second contact hole and covering the inorganic insulating film exposed at the bottom of the second contact hole. The step (g) is to form the pixel electrode covering the organic resin insulating film and covering the inner wall of the pixel-drain contact hole and the contact conductor film. [0022] According to the electro-optic display manufacturing method, in the step (e), an ashing process using oxygen is performed to thin the entire organic resin insulating film and to process the second opening to make its inner walls smoothly slope to be like a crater in cross section with its opening increasing in size from the bottom toward the opening end, so as to form the second contact hole passing through the organic resin insulating film. This structure prevents disconnection of the pixel electrode within the pixel-drain contact hole. Continue reading... Full patent description for Electro-optic display and manufacturing method thereof Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electro-optic display and manufacturing method thereof patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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